1. Field of the Invention
The invention relates to a suspension system for land vehicles, in particular non-track-bound motor vehicles, with a sensor system which detects the actual values of the positions of the vehicle wheels relative to the vehicle body or chassis and longitudinal and/or transverse accelerations of the vehicle, and with a ride-height control system which controls control elements or assemblies so as to change the actual position of the wheels as a function of a set/actual value comparison between variably specifiable set values for the positions of the wheels and averages over time of the actual values of the abovementioned positions.
2. Description of the Related Art
A suspension system of this kind forms the subject-matter of DE 41 38 831 A1. Here, the signals representing the longitudinal and transverse accelerations of the vehicle are processed in such a way that the pitching or rolling angle of the body during longitudinal or transverse acceleration is reduced.
Suspension systems of the abovementioned type can be of numerous different design configurations.
For example, a vehicle can have any passive suspension system, for example one with mechanical springs and, in parallel with this, a controllable additional suspension system, by means of which additional forces dependent on the vehicle loading can be produced in order to keep the vehicle body at a specified level relative to the vehicle wheels, to a very large extent independently of disturbing forces.
The prior art also includes pneumatic spring systems whose pneumatic spring units, generally pneumatic bellows, can be connected to a pneumatic pressure source and/or to atmosphere by a corresponding control system, making it possible to establish a specified level by supplying or discharging air to or from the pneumatic spring unit.
In hydropneumatic suspension systems, hydraulic displacer units are arranged between the vehicle body and the vehicle wheels, their displacer working space communicating with a, generally pneumatic, spring energy store. The vehicle body can be raised or lowered relative to the wheels or to individual wheels by supplying or discharging hydraulic medium to or from the hydraulic displacer unit, thus once again allowing a specified level to be established.
Finally, it is possible on fundamentally any suspension systems, particularly those with mechanical spring elements, to arrange in series with each or with specified spring elements a hydraulic displacer unit which forms an adjustable body-side or wheel-side abutment for the respective spring element. Here, it is possible, by supplying or discharging hydraulic medium, to perform adjustment of the height of the body relative to the respective vehicle wheels and hence to achieve ride-height control.
To keep down the control outlay required and, in particular, the power requirement for the control elements or assemblies for changing the actual position of the wheels relative to the body, DE 3525367 Al discloses subjecting the actual-value signals for the position of the vehicle wheels relative to the body to low-pass filtering. This ensures that only correspondingly slow or prolonged level changes are eliminated and that the control system does not respond to normal suspension travel. Here, use is made of the fact that low-pass filtering of a signal leads to averaging of the signal over time, the period of time over which the averaging is carried out being determined by the limit frequency of the low-pass filter.
The present invention is directed towards one or more of the problems set forth above.